Control device of vehicular fuel cell system and related method

ABSTRACT

A control device for a vehicular fuel cell system is provided with a warm-up output control section operative, when a fuel cell system is started up under a low temperature condition and in case that a fuel cell stack of the fuel cell system is warmed up, causing the fuel cell stack to generate electric power to allow predetermined warm-up electric power to be taken out, and a run permission section operative, during a period wherein the warm-up electric power is drawn by the warm-up output control section, to determine whether the fuel cell stack assumes a predetermined warm-up condition on the basis of one of a voltage value and an electric current value of the fuel cell stack. When a determination is made that the fuel cell stack assumes the predetermined warm-up condition, the run permission section provides a vehicle with run permission.

TECHNICAL FIELD

The present invention relates to a control device of vehicular fuel cellsystem and a related method and, more particularly, to a control deviceof a vehicular fuel cell system that permits a fuel cell stack togenerate electric power at less power than a rated electric power duringstart-up at a low temperature condition, thereby warming up the fuelcell system, and a related method.

BACKGROUND

Japanese Patent Application Laid-Open Publication No. 2002-305013discloses a vehicular fuel cell system which, during start-up of avehicle at a low temperature condition such as a below-freezingtemperature, permits a fuel cell stack to generate electric power at apredetermined power to achieve warm-up of a fuel cell prior tocommencement to travel the vehicle, and which discriminates to findwhether the warm-up of the fuel cell stack has been completed, referringto an air electrode (cathode) exhaust gas temperature, a temperaturedifference between an air electrode intake air and an air electrodeexhaust, and a temperature factor such as a temperature of coolant,thereby providing the vehicle with a run permission (see FIG. 3 and itsrelated description).

SUMMARY OF INVENTION

However, upon careful studies conducted by the present inventors, insuch a vehicular fuel cell system, because a fuel cell stack larger thanthat of a domestic electric power supply is provided to supply a vehicledrive electric power, a result is an increase in an uneven temperaturedistribution between a central stack portion and a terminal stackportion. It is conceivable that, depending upon conditions, such as anoutput of the fuel cell stack, occurring during an initial stage ofstart-up and at warm-up completion, it is difficult to correctlydetermine, based on only a temperature factor, whether a warm-up of thefuel cell stack has been completed.

Further, although it is conceivable to use a structure wherein adetermination is made whether the warm-up has been completed using ahighly accurate temperature sensor, because such a structure needs tomake a determination on the basis of an increased temperature value,while considering safety in the presence of an unevenness in temperaturevalues, detected by the temperature sensor, a tendency tends to occur inwhich time, energy, and the amount of fuel consumed during warm-up,which are needed before making a judgment whether warm-up has beencompleted, energy and the amount of fuel consumed during warm-upincrease.

The present invention has been completed upon such studies conducted bythe present inventors and, specifically, has an object to provide acontrol device for a vehicular fuel cell system and its related methodthat enable a time needed before making judgment to find whether warm-uphas been completed to be minimized and the energy required for warm-upto be saved to thereby improve fuel saving performance of a fuel cellpowered vehicle.

To achieve the above object, according to one aspect of the presentinvention, a control device of a vehicular fuel cell system includes: awarm-up output control section operative, when a fuel cell system isstarted up under a low temperature condition and in case that a fuelcell stack of the fuel cell system is warmed up, causing the fuel cellstack to generate electric power to allow predetermined warm-up electricpower to be drawn; and a run permission section operative, during aperiod wherein the warm-up electric power is drawn by the warm-up outputcontrol section, to discriminate whether the fuel cell stack assumes apredetermined warm-up condition on the basis of one of a voltage valueand an electric current value of the fuel cell stack, whereby whendiscrimination is made that the fuel cell stack assumes thepredetermined warm-up condition, the run permission section provides avehicle with run permission.

Stated in another way, according to another aspect of the presentinvention, a control device of a vehicular fuel cell system includes: awarm-up output controlling means, when a fuel cell system is started upunder a low temperature condition and in case that a fuel cell stack ofthe fuel cell system is warmed up, for controlling the fuel cell stackto generate electric power to allow predetermined warm-up electric powerto be drawn; and a run permission providing means, while discriminatingwhether the fuel cell stack assumes a predetermined warm-up condition onthe basis of one of a voltage value and an electric current value of thefuel cell stack during a period wherein the warm-up electric power isdrawn by the warm-up output controlling means, for providing a vehiclewith run permission when discrimination is made that the fuel cell stackassumes the predetermined warm-up condition.

On the other hand, according to another aspect of the present invention,a method of controlling a vehicular fuel cell system, the methodincludes the steps of: taking out predetermined warm-up electric powerby controlling the fuel cell stack to generate electric power, when afuel cell system is started up under a low temperature condition and incase that a fuel cell stack of the fuel cell system is warmed up; andproviding a vehicle with run permission when discrimination is made thatthe fuel cell stack assumes a predetermined warm-up condition, whilediscriminating whether the fuel cell stack assumes the predeterminedwarm-up condition on the basis of one of a voltage value and an electriccurrent value of the fuel cell stack during a period wherein the warm-upelectric power is drawn.

Other and further features, advantages, and benefits of the presentinvention will become more apparent from the following description takenin conjunction with the following drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating a schematic structure of avehicular fuel cell system of a first embodiment according to thepresent invention;

FIG. 2 is a system structural view illustrating a further concretestructure of the fuel cell system of the presently filed embodiment;

FIG. 3 is a block diagram illustrating a structure of an electricalsystem of the fuel cell system shown in FIG. 2;

FIG. 4 is a flowchart illustrating a sequence of flows in start-upoperation to be executed by a control device of the fuel cell system ofthe presently filed embodiment;

FIG. 5 is a timing chart illustrating variations in time of stackoutput, stack voltage, and coolant temperature during execution ofstart-up operation shown in FIG. 4;

FIG. 6 is a view illustrating the relationship between stack current andrun available voltage of the presently filed embodiment;

FIG. 7 is a view illustrating current/voltage characteristics of thefuel cell stack accompanied by warm-up operation, andcurrent/stack-output characteristics associated with respectivecurrent/voltage characteristics of the presently filed embodiment;

FIG. 8 is a flowchart illustrating a sequence of flows in start-upoperation to be executed by a control device of a vehicular fuel cellsystem of a second embodiment according to the present invention;

FIG. 9 is a timing chart illustrating variations in time of stackoutput, stack voltage and coolant temperature during execution ofstart-up operation shown in FIG. 8; and

FIG. 10 is a view illustrating the relationship between stack voltageand run available current of the presently filed embodiment.

DETAILED DESCRIPTION

A controller device for a vehicular fuel cell system and its relatedmethod of each of various embodiments according to the present inventionare described in detail herein with suitable reference to theaccompanying drawings.

First Embodiment

First, referring to FIGS. 1 to 7, a control device of a vehicular fuelcell system and its related method of a first embodiment according tothe present invention are described below in detail.

FIG. 1 is a block diagram showing a schematic structure of the vehicularfuel cell system of the presently filed embodiment.

In FIG. 1, the vehicular fuel cell system S can include a fuel cellstack 1 that is supplied with fuel gas (hydrogen containing gas) and air(oxygen containing gas) to generate electric power, an inverter 2converting DC power delivered from the fuel cell stack 1 to AC power, adrive motor 3 supplied with AC power from the inverter 2 to drive wheelsWH of a vehicle VH, an auxiliary device 4 that supplies the fuel cellstack 1 with air and coolant, an ammeter 5 that detects electric currentof electric power generated by the fuel cell stack 1, a voltmeter 6 thatdetects voltage of electric power generated by the fuel cell stack 1,and a vehicle controller 9 that allows the vehicle to travel dependingupon a run permission provided by a control device 10.

The control device 10 is comprised of a warm-up output control section 8operative to cause the fuel cell stack 1 to generate electric power toallow warm-up electric power to be drawn at a predetermined amountduring start-up of the fuel cell stack 1 under a low temperaturecondition, and a run permission section 7 that provides the vehiclecontroller 9 with run permission in case that it is determined that thefuel cell stack 1 has reached a predetermined warmed up condition, basedon detected values resulting from the ammeter 5 and the voltmeter 6 whenwarm up output is drawn at a predetermined amount by the warm-up outputcontrol section 8. In particular, the run permission section 7 sends arun permission signal RSIG to the vehicle controller 9; the warm-upoutput control section 8 sends a warm-up start signal WSIG to the runpermission section 7 and an auxiliary drive signal ASIG (A1SIG and A2SIGin FIG. 3) to the auxiliary unit 4; and the vehicle controller 9 sends amotor drive signal MSIG to the inverter 2 and a vehicle demanded powersignal PSIG to the warm-up output control section 8. Also, the auxiliarydevice 4 is supplied with an auxiliary device drive signal ASIG (A3SIGand A4SIG in FIG. 3) from the vehicle controller 9.

Structure of Vehicular Fuel Cell System

Now, referring to FIGS. 2 and 3, a structure of the vehicular fuel cellsystem to which such a control device 10 is applied is described indetail.

The fuel cell system generally can include an air system through whichair is supplied to the fuel cell stack, a hydrogen system through whichhydrogen gas is supplied to the fuel cell stack, a coolant system bywhich the fuel cell stack is cooled, and an electrical system throughwhich operation of the system is controlled. Therefore, hereinafter, thestructure of the fuel cell system is described in detail for eachsystem.

FIG. 2 is a system structural view illustrating a further structure ofthe fuel cell system of the presently embodiment, and FIG. 3 is a blockdiagram illustrating a structure of the electrical system of the fuelcell system shown in FIG. 2.

Structure of Air System

As shown in FIG. 2, the air system AS includes a compressor 12 thatcompresses air that is drawn through a flow meter 11, an air temperatureregulator 13 that regulates the temperature of compressed air, and amoisture exchanger unit 15 operative to humidify air at a regulatedtemperature and to supply the air to an air electrode (cathode) supplymanifold 14 a of the fuel cell stack 14 (corresponding to the fuel cell1 shown in FIG. 1).

Here, the moisture exchanger unit 15 removes moisture from airdischarged from an air electrode output manifold 14 b of the fuel cellstack 14 and allows recovered moisture to be added to air being suppliedto the air electrode. Also, disposed between the air electrode supplymanifold 14 a and the moisture exchanger unit 15 is a pressure sensor 16by which the pressure of air being supplied to the fuel cell stack 14 ismeasured.

Further, the air system includes a pressure control valve 17 that isconnected to an off-gas supply port of the moisture exchanger unit 15and regulates the pressure of air discharged from the air electrodeoutlet manifold 14 b of the fuel cell stack 14. Air, whose pressure isregulated with the pressure control valve 17, is introduced to acombustor 18, wherein air and anode off-gas, which is separatelyintroduced, combust and exhaust gases are expelled to the atmosphere.

Moreover, the combustor 18 can include an electric-heated catalystsection 18 a that is heated to a catalyst activity temperature withelectrical heat, a catalytic combustor section 18 b that enablescombustion of anode off-gas and air, and a heat exchanger 18 c thatallows combustion heat to be transferred to coolant, and theelectric-heated catalyst section 18 a, with the electric-heated catalystsection 18 a and the catalytic combustor section 18 b incorporatingtemperature sensors 18 d, 18 e for detecting temperatures, respectively.

Structure of Hydrogen System

As shown in FIG. 2, the hydrogen system HS can include a hydrogentemperature regulator 23 for regulating the temperature of hydrogen gasbeing supplied from a hydrogen tank 22 through a shut-off valve 21, apressure regulator valve 24 for regulating the pressure of hydrogen gaswith regulated temperature, and an ejector 26 for supplying a hydrogenelectrode (anode) supply manifold 14 c of the fuel cell stack 14 withhydrogen gas supplied from the pressure regulator valve 24 through theflow meter 25.

Here, disposed between the hydrogen electrode supply manifold 14 c andthe ejector 26, is a pressure sensor 27 for measuring the pressure ofhydrogen gas to be supplied to the fuel cell stack 14. Also, hydrogengas discharged from the hydrogen electrode outlet manifold 14 d of thefuel cell stack 14 is returned to the ejector 26 again and mixed withhydrogen gas supplied through the flow meter 25, with the resultingmixture being supplied again to the fuel cell stack 14.

Further, disposed between a hydrogen electrode outlet manifold 14 d andthe ejector 26 is a branch passage in which a purge valve 28 is disposedfor permitting anode gas, containing impurities such as nitrogen, to bepurged. Hydrogen gas purged from the purge valve 28 is combusted in thecombustor 18, and combustion gases are exhausted to the atmosphere.

Structure of Coolant System

As shown in FIG. 2, the coolant system CS can include a radiator 32having a fan 31 adapted to be rotationally driven to cool coolant, athree-way valve 34 arranged to supply coolant to a coolant inletmanifold 14 e of the fuel cell stack 14 through a shut-off valve 33, acoolant pump 35 by which coolant, discharged from coolant outletmanifold 14 f of the fuel cell stack 14, can be circulated, and atemperature sensor 36 for measuring the temperature Tso [° C.] ofcoolant discharged from the coolant outlet manifold 14 f.

Here, the three-way valve 34 is enabled to control the flow rate ofcoolant that is branched off at a branch point 37 in a direction towardthe radiator 32 and in a direction toward a heat exchanger 18 c. Also,the three-way valve 34 is enabled to supply coolant to the airtemperature regulator 13 and the hydrogen temperature regulator 23 via abranch point 38.

Structure of Electrical System

As shown in FIG. 3, the electrical system ES includes a fuel cell powerplant 41, which is comprised of the fuel cell stack 14, a high powerauxiliary device 41 a, such as an inverter for the compressor, and a lowpower auxiliary device 41 b.

Further, the electrical system includes a junction box (JB) 43 thatprovides electric power from the fuel cell stack 14 to a power manager42, the junction box 43 including a current sensor 43 a and a voltagesensor 43 b which detects electric current (hereinafter referred to asstack current) Is [A] of the fuel cell stack 14 and a voltage(hereinafter referred to as stack voltage) Vs [V], respectively.

Here, the power manager 42 serves to allow electric power, deliveredfrom the junction box 43, to be supplied to an inverter 45(corresponding to an inverter 1 in FIG. 1) for a drive motor 44(corresponding to the drive motor 33 in FIG. 3) of the vehicle, avehicle high power auxiliary device 46 such as an air conditionersystem, a secondary battery 47 and the high power auxiliary device 41 a.

Further, the power manager 42 renders a DC/DC converter 48 to step downin voltage of electric power, supplied from the junction box 43, andpermits resulting electric power to be supplied to the low powerauxiliary device 41 b, a low power battery 49 for the low powerauxiliary device, and a vehicle weak current auxiliary device 50. Also,the current sensor 43 a and the voltage sensor 43 b correspond to theammeter 5 and the voltmeter 6, respectively, in FIG. 1.

Furthermore, the electrical system also includes a fuel cell power plantcontroller 52 (corresponding to the control device 1 in FIG. 1) that isresponsive to stack current Is, stack voltage Vs and the vehicledemanded power signal PSIG, which is inputted from a vehicle controller51 (corresponding to the vehicle controller 9 in FIG. 1), and appliesthe drive signals to the high power auxiliary device 41 a and the lowpower auxiliary device 41 b while inputting the run permission signalRSIG to the vehicle controller 51. Here, the vehicle controller 51 isresponsive to the run permission signal RSIG to allow the drive signalsto be inputted to the inverter 45, the vehicle high power auxiliarydevice 46 and the vehicle weak current auxiliary device 50.

Moreover, the vehicle controller 51 serves to generate the vehicledemanded power signal PSIG, representative of a demanded electric power,referring to an SOC signal, indicative of a charged status of thebattery, which is outputted from the secondary battery 47.

Also, the above-described auxiliary devices 41 a, 41 b, 46, 50correspond the auxiliary device 4 shown in FIG. 1.

Besides, the current sensor 43 a transmits a stack current signal ISIG,representative of electric current flowing through the fuel cell stack14, to the fuel cell power plant controller 52, to which a stack voltagesignal VSIG, representative of output voltage of the fuel cell stack 14,is applied from the voltage sensor 43 b. The secondary battery 47applies the SOC signal SOCSIG, representative of resulting SOC, to thevehicle controller 51. The vehicle controller 51 delivers the motordrive signal MSIG to the inverter 45, the vehicle demanded power signalPSIG to the fuel cell power plant controller 52, the drive signal A3SIGto the vehicle high power auxiliary device 46 and the drive signal A4SIGto the vehicle weak current auxiliary device 50. The fuel cell powerplant controller 52 is operative to apply the run permission signal RSIGto the vehicle controller 51, the drive signal A1SIG to the high powerauxiliary device 41 a and the drive signal A2SIG to the low powerauxiliary device 41 b.

Operation of Vehicular Fuel Cell System

Now, referring to FIGS. 4 to 10, description is made of how thevehicular fuel cell system S with the structure set forth above operatesduring start-up.

FIG. 4 is a flowchart illustrating the flow of start-up operation of thecontrol device of the fuel cell system of the presently filedembodiment, FIG. 5 is a timing diagram illustrating changes in time ofstack output, stack voltage and coolant temperature during start-upoperation being executed as shown in FIG. 4, FIG. 6 is a viewillustrating the relationship between stack current and run availablevoltage of the presently filed embodiment, and FIG. 7 is a viewillustrating current/voltage characteristics and current/stack-outputcharacteristics, corresponding to the respective current/voltagecharacteristics of the fuel cell stack, accompanied by warm-up operationbeing executed, in the presently filed embodiment.

First, referring to the flowchart shown in FIG. 4 and the timing diagramshown in FIG. 5, detailed description is made of how start-up operation(in a warm-up mode) is executed in the vehicular fuel cell system of thepresently filed embodiment.

The flowchart shown in FIG. 4 illustrates control operation of the fuelcell power plant controller 52, which responds to a start-up request,initiated by a key switch which is not shown, and begins to execute astart-up operation (at time T=0 as shown in FIG. 5) that proceeds tostep S1.

In step S1, immediately after start-up of the fuel cell system, becausethe fuel cell power plant controller 52 and, more particularly, the runpermission section 7 (see FIG. 1) are unable to determine whether thefuel cell stack 14 is available to supply electric power needed to causethe vehicle to travel the fuel cell power plant controller 52 turns offthe vehicle run permission signal RSIG, and operation is routed to stepS2.

In next step S2, the fuel cell power plant controller 52 and, moreparticularly, the warm-up output control section 8 (see FIG. 1) drivethe coolant pump 35, thereby commencing circulation of coolant. Also,when this takes place, the three-way valve 34 controls the flow path ofcoolant such that coolant is circulated between the fuel cell stack 14and the heat exchanger 18 c of the combustor 18.

In succeeding step S3, the warm-up output control section 8 retrieves adetected value of the temperature sensor 36, thereby detecting atemperature Tso of coolant discharged from the coolant outlet manifold14 f.

In subsequent step S4, the warm-up output control section 8 determineswhether the detected coolant temperature Tso is equal to or higher thana predetermined temperature Ts required for warming up the fuel cellstack 14, thereby making a judgment whether during start-up of thevehicle, the fuel cell stack 14 needs a warm-up operation. Incidentally,even though the temperature Ts depends upon a performance of the fuelcell stack 14, the warm-up output control section 8 determines that,since an output performance required for travel of the vehicle can beensured in the presence of the coolant temperature Tso equal to orhigher than the temperature Ts (in the vicinity of 20 [° C.]) at whichthere is surely no need for warm-up, there is no need for warm-up of thefuel cell system 14.

If the warm-up output control section 8 determines that the detectedcoolant temperature Tso is equal to or exceeds the temperature Tsnecessary for warm-up of the fuel cell stack 14 and no need arises forwarm-up of the fuel cell stack 14, the start-up operation proceeds tostep S11. On the contrary, if the warm-up output control section 8determines that the detected coolant temperature Tso remains less thanthe temperature Ts at which the fuel cell stack 14 needs to be warmedup, and there is a need for executing warm-up of the fuel cell stack 14,the warm-up start signal WSIG is delivered from the warm-up outputcontrol section 8 to the run permission section 7, the start-upoperation proceeds to step S5.

In step S5, the warm-up output control section 8 detects the vehicledemanded power signal PSIG, representative of the demanded power, whichis outputted from the vehicle controller 51. Incidentally, when thistakes place, since no run permission signal PSIG is outputted from therun permission section 7 as a result of operation in step S1, no requestfor power required for the vehicle to travel is involved in the vehicledemanded power signal PSIG that involves only a request for powerrequired for vehicle auxiliary devices to be driven, such as an airconditioner and a window defogger system. When this takes place, theoperation in step S5 is completed, and the start-up operation is routedfrom step S5 to step S6.

In subsequent step S6, the warm-up output control section 8 calculatesan airflow rate required for the fuel cell stack 14 to generate electricpower at an amount demanded for driving the vehicle auxiliary devices.Incidentally, during a period in which the vehicle is inhibited fromtraveling, no probability occurs for the amount of electric powerdemanded for the fuel cell stack 14 to exceed a total value of themaximum electric power to be consumed by the auxiliary devices.Accordingly, the warm-up output control section 8 calculates the airflowrate necessary for electric power to be obtained at an amountapproximately in the order of this total value (e.g., 10 [kW]).

In addition, the warm-up output control section 8 calculates the airflowrate necessary for the combustor 18 to remain at or below apredetermined combustion temperature by taking oxygen content, to beconsumed for generation of electric power, into consideration. Due tothe presence of the fuel cell stack 14 and the combustor 18 connected inseries, the warm-up output control section 8 calculates a flow rate ofair, to be discharged from the compressor 12, in order to realize theairflow rate that is needed for the fuel cell stack 14 and the combustor18. When this takes place, the operation of step S6 is completed, andthe start-up operation proceeds from step S6 to step S7.

In succeeding step S7, the warm-up output control section 8 controls theauxiliary devices 41 a, 41 b inside the fuel cell power plant controller41 to cause the fuel cell stack 14 to be heated and warmed up. Moreparticularly, the warm-up output control section 8 controls therotational speed of the compressor 12 depending upon the requisitedischarge airflow rate. Also, the warm-up output control section 8 turnson the electric-heated catalyst section 18 a in response to a drop inthe temperature of the electric-heated catalyst section 18 a so that itis equal to or less than the predetermined temperature necessary forignition in the combustor. Additionally, the warm-up output controlsection 8 controls the pressure control valves 17, 24, respectively, soas to allow air and hydrogen gas to remain in predetermined pressurelevels, respectively. Moreover, the warm-up output control section 8controls the purge valve 28, thereby controlling the flow rate ofhydrogen gas to be supplied to the combustor 18. Additionally, thewarm-up output control section 8 controllably drives the coolant pump 35such that the heat exchanger 18 c achieves heat exchange between theheat resulting from the catalytic combustor 18 b and coolant to enablethe fuel cell stack 14 to be heated with the resulting heat. When thistakes place, the operation of step S7 is completed, and the start-upoperation proceeds from step S7 to step S8.

In consecutive step S8, the run permission section 7 detects stackcurrent Is and stack voltage Vs resulting in the fuel cell stack 14using the current sensor 43 a and the voltage sensor 43 b, respectively.When this takes place, the operation in step S8 is completed, and thestart-up operation proceeds from step S8 to step S9.

In next step S9, the run permission section 7 retrieves run availablevoltage Va [kW], in terms of detected stack current Is, referring to thecurrent/voltage characteristics shown in FIG. 6, representative of therelationship between stack current Is and stack voltage (run availablevoltage or run permission voltage) at which the vehicle is available totravel. When this takes place, the operation in step S9 is completed,and the start-up operation proceeds from step S9 to step S10.Incidentally, the current/voltage characteristics shown in FIG. 6 isstored as a map in a memory, which is not shown, in the fuel cell powerplant controller 52.

In consecutive step S10, the run permission section 7 determines whetherdetected stack voltage Vs is equal to or exceeds run available voltageVa, thereby determining whether the fuel cell stack 14 has beencompletely warmed up. If the detected stack voltage Vs is found to beless than run available voltage Va and the warm-up output controlsection 8 determines that the fuel cell stack 14 has not been completelywarmed up, the run permission section 7 allows start-up operation toreturn to step S5. On the contrary, if the detected stack voltage Vs isfound to be equal to or exceed run available voltage Va the warm-upoutput control section 8 determines that the fuel cell stack 14 has beencompletely warmed up and the run permission section 7 allows thestart-up operation to proceed to step S11.

In succeeding step S11, the run permission section 7 outputs the runpermission signal RSIG, permitting the vehicle to travel, to the vehiclecontroller 51 (at time T=T1 in FIG. 5). When this takes place, a seriesof start-up operations (in warm-up travel mode shown in FIG. 5) arecompleted and, thereafter, the fuel cell power plant controller 52executes operation (in a normal travel mode as shown in FIG. 5) by whichthe fuel cell power plant 41 is controlled so as to generate electricpower depending upon the demanded electric power at the amount requiredfor the vehicle to travel. Incidentally, in FIG. 5, the output Ps [kW]of the fuel cell stack 14 represents certain electric power Psw [kW],before start-up during a warm-up and travel mode, and electric power Psn[kW] required for the vehicle to travel during a normal travel mode.

Concept of Start-Up Operation

Next, referring also to FIG. 7, detailed description is made of aconcept of executing start-up operation set forth above. Incidentally,in FIG. 7, a left ordinate, a right ordinate and an abscissa representstack voltage Vs [V], stack output Ps [kW] and stack current Is [A],respectively, and solid lines and broken lines represent current/voltagecharacteristics A, B, C of the fuel cell stack 14 andcurrent/stack-output characteristics A′, B′, C′ in terms of therespective current/voltage characteristics.

Further, the characteristics A, A′, at which stack voltage and stackcurrent take the lowest values, represent characteristics at anextremely low temperature (at minus twenty degrees) at which the fuelcell stack 14 needs to be warmed up; the characteristics B, B′, at whichstack voltage and stack current take next lower vales, representcharacteristics with the temperatures at which the stack output value isavailable to provide the vehicle with run permission; andcharacteristics C, C′, at which stack voltage and stack output valuetake the highest vales, represent characteristics with the temperatureat which the maximum performance of the fuel cell stack is obtained.

Now, considering a case where immediately after the warm-up has begun,the fuel cell stack 14 exhibits the characteristics A, A′, even ifattempt is made to draw stack current Is from the fuel cell stack 14, adrop occurs in stack voltage Vs and, hence, it is hard to promptlyobtain the stack output value Pr that enables run permission to beprovided to the vehicle. Such a circumstance can be determined from themagnitudes in stack current Is and stack voltage Vs when generation ofelectric power Psw (in the order of approximately 10 [kW]) duringwarm-up operation and, in an exemplary case shown in FIG. 7, the fuelcell stack 14 merely operates at stack current Is =I1 and stack voltageVs=V1 so as to obtain generated electric power Psw.

However, with the fuel cell stack 14 being progressively warmed up,stack voltage Vs gradually rises and, at the characteristics B, B′, thefuel cell stack 14 is enabled to provide the stack output value Pravailable to allow a run permission to be provided in the presence ofstack current value remaining at Ir. Although stack current Is and stackvoltage Vs for obtaining generated electric power Ps at thecharacteristics B can be generally expressed to lie at I2 and V2,respectively, run available voltage Va, associated with stack current Iravailable to obtain the stack output Pr that enables run permission tobe provided, lies at a value Vr.

Incidentally, although no need arises for retrieving run availablevoltage Va provided that generated electric power Ps during warm-upremains constant, a probability occurs in which generated electric powerPs varies depending upon the status of the auxiliary device duringwarm-up. Even in such a case, by retrieving run available voltage Va,associated with stack current Is, referring to the characteristics B, itis possible to correctly determine whether to provide the vehicle with arun permission.

As set forth above, with the structure of the presently filedembodiment, the fuel cell power plant controller 52 operates such that,when a determination is made that the fuel cell stack has reached apredetermined warmed-up condition based on the detected values incurrent and voltage of the fuel cell stack, during operation in whichthe fuel cell stack 14 is made operative to generate electric power toallow predetermined warm-up power output to be drawn during start-up ofthe fuel cell stack 14 at the low temperature, the fuel cell power plantcontroller 52 outputs the run permission signal, permitting the vehicleto travel, to the vehicle controller 51.

When this takes place, since the fuel cell power plant controller 52 isable to accurately determine that a situation occurs in which a stackoutput necessary for the vehicle to travel can be ensured, the fuel cellpower plant controller 52 is able to correctly perform a judgmentwhether to permit the vehicle to travel, while minimizing a waste oftime, needed before the vehicle commences to travel, and energyconsumption.

Further, the fuel cell power plant controller 52 detects stack voltageVs whereupon a determination is made such that the vehicle is availableto travel when the stack voltage Vs equals or exceeds the predeterminedvalue needed before the vehicle commences travel, resulting in theminimization of wasted time and energy consumption, and a simplifiedstructure.

Furthermore, since the fuel cell power plant controller 52 is operativeto determine a value of the voltage, based on which run permission is tobe judged, depending upon the current value of generated electric powerduring warm-up, the fuel cell power plant controller 52 is able tocorrectly determine whether to permit the vehicle to travel even in thepresence of transitions in generated electric power during warm-up.

Moreover, with the vehicular fuel cell system on which a secondarybattery of a large capacity is specifically installed, since a largeproportion of electric power required for the vehicle to travel can bebacked by the secondary battery, it becomes possible for the vehicle tobe suitably provided with run permission even at the low temperaturecondition where no electric power is generated by the fuel cell.

Additionally, with the fuel cell system using a fuel cell having aporous plate especially containing water, while warm-up continues toremove water at a below-freezing temperature, it becomes possible toobtain a fuel cell output that makes it possible to provide the vehiclewith a run permission even in the course of thawing such ice.

In addition, with the fuel cell system using the fuel cell having such aporous plate, cathode exhaust gas and coolant outlet temperatures remainconstant in the vicinity of 0 [° C.], in case of determining whether toprovide the vehicle with run permission by detecting the temperaturerise, the fuel cell system has no choice but to make decision under acondition where the cathode exhaust gas and coolant outlet temperaturesexceed a value of 0 [° C.] (above 5 [° C.]). Consequently, with such astructure, in case where freezing occurs with water inside the porousplate at the below-freezing temperature, it is hard for the fuel cellsystem to provide the vehicle with run permission until ice is fullythawed and, hence, much time and energy are needed before the vehiclebecomes available to travel. However, when applied with the structure ofthe presently filed embodiment, since the fuel cell system is able toaccurately perform judgment whether to provide the vehicle with runpermission even under a situation where cathode exhaust gas and coolantoutlet temperatures remain constant in the vicinity of 0 [° C.], wastedtime and energy consumption, required before the vehicle is permitted torun, can be minimized.

Second Embodiment

Now, referring to FIGS. 8 to 10, a detailed description is made of acontrol device of a vehicular fuel cell system and its related method ofa second embodiment according to the present invention.

FIG. 8 is a flowchart showing the flow of start-up operation of acontrol device of a fuel cell system of the presently filed embodiment;FIG. 9 is a timing diagram illustrating variations in stack output,stack voltage and coolant temperature in terms of time during executionof start-up operation shown in FIG. 8; and FIG. 10 is a viewillustrating the relationship between stack voltage and run availablecurrent of the presently filed embodiment. Also, start-up operation ofthe presently filed embodiment is executed in the same manner as that ofthe first embodiment shown in FIG. 1 except for operations in step S9and step S10. Therefore, in the following description, description ismainly made of operations in step S9 a and step S10 a, associated withstart-up operation of fuel cell system of the second embodiment, whichcorrespond to step S9 and step S10, respectively, with remaining othersteps being omitted or simplified in description. Also, thevoltage/current characteristics shown in FIG. 10 serves as a map that isstored in a memory, which is not shown, in the fuel cell power plantcontroller 52.

As shown in FIG. 8, as a start-up operation in the presently filedembodiment is commenced and operation proceeds, operation in step S9 ais commenced depending upon completion of operation in step S8.

In step S9 a, the fuel cell power plant controller 52 retrieves a runavailable current Ia in terms of detected stack voltage Vs, referring tothe current/voltage characteristics, shown in FIG. 10, representative ofthe relationship between stack voltage Vs and stack current (runavailable current or run permission current) Ia at which the vehicle isavailable to travel. When this takes place, operation of step S9 iscompleted, and start-up operation proceeds from step S9 a to step S10 a.

In subsequent step S10 a, the fuel cell power plant controller 52discriminates whether the detected stack current Is is equal to or lessthan run available current Ia, thereby making judgment whether the fuelcell stack 14 has been completely warmed up. If detected stack currentIs is found to be equal to or less than run available current Ia and thewarm-up of the vehicle is found to be completed, then, the fuel cellpower plant controller 52 allows start-up operation to proceed to stepS11. On the contrary, if detected stack current Is is found not to beequal to or less than run available current Ia and warm-up of thevehicle is found not to be completed, then, the fuel cell power plantcontroller 52 allows start-up operation to proceed to step S5.Incidentally, the reason why the determination whether fuel cell stack14 has been completely warmed up is executed at a time when stackcurrent Is becomes equal to or less than run available current Ia isthat the presence of a drop occurring in electric current, required forobtaining the output Ps during warm-up, enables an increase in voltageto be discriminated.

As set forth above, with the structure of the presently filedembodiment, the fuel cell power plant controller 52 is operative toallow the fuel cell stack 14 to generate electric power such thatwarm-up electric power is available to be taken out at the predeterminedamount during start-up of the fuel cell stack 14 under the lowtemperature condition while compelling the run permission signal,permitting the vehicle to travel, to be outputted to the vehiclecontroller 51 in response to the occurrence of the current/voltagecharacteristics of the fuel cell stack assuming a predeterminedcondition during a period in which warm-up electric power is drawn. Whenthis takes place, since the fuel cell power plant controller 52 is ableto accurately discriminate to find that a situation exists wherein stackoutput required for the vehicle to travel is ensured, the fuel cellpower plant controller 52 is able to correctly perform a judgmentwhether to provide a run permission to the vehicle, while minimizingtime and energy consumption that can result before the vehicle commencestravel.

Further, since the fuel cell power plant controller 52 detects stackcurrent Is resulting from predetermined electric power being generatedand determines that the vehicle is available to travel, depending uponthe occurrence of stack current Is remaining equal to or less than thepredetermined value, a simplified structure is provided and it ispossible to minimize time and energy consumption that result before thevehicle commences travel.

Furthermore, since the fuel cell power plant controller 52 is operativeto determine a determining value of electric current, based on which runpermission is to be judged, depending upon the voltage value resultingfrom electric power generated during warm-up, the fuel cell power plantcontroller 52 is able to accurately determine whether to allow thevehicle to be provided with run permission even in the presence oftransitions in electric power during warm-up.

Incidentally, with the various embodiments set forth above, nolimitation is intended by the present invention for the method ofestimating stack current Is and stack voltage Vs and these factors maybe estimated in other ways.

Further, in case where electric power generated by the fuel cell stack14 during warm-up remains substantially constant, no run availablevoltage Va in terms of stack current Is may be retrieved, and runavailable voltage Va may be kept at a fixed value. Also, similarly, incase where electric power generated by the fuel cell stack 14 remainssubstantially constant during warm-up, no run available current Ia interms of stack voltage Vs may be retrieved, and run available current Iamay be kept at a fixed value.

With the structure of the present invention set forth above, dependingupon the voltage value or the current value of the fuel cell stack whentaking out electric power from the fuel cell stack at an amount lessthan that a rated power output during warm-up of the fuel cell stack, adetermination is made whether the fuel cell stack assumes apredetermined warm-up condition, and an advantageous effect resides inthat warm-up completion decision can be accurately made based on theelectrical characteristics of the fuel cell stack whereby time, beforewarm-up completion is decided, can be minimized and energy required forwarm-up can be saved, thereby enabling a fuel saving performance of afuel cell powered vehicle to be highly improved.

The entire content of a Patent Application No. TOKUGAN 2003-089089 witha filing date of Mar. 27, 2003 in Japan is hereby incorporated byreference.

Although the invention has been described above by reference to certainembodiments of the invention, the invention is not limited to theembodiments described above. Modifications and variations of theembodiments described above will occur to those skilled in the art, inlight of the teachings. The scope of the invention is defined withreference to the following claims.

INDUSTRIAL APPLICABILITY

As set forth above, the control device of the vehicular fuel cell systemof the present invention and its related method includes the structurethat, while drawing a predetermined warm-up electric power bycontrolling the fuel cell stack to generate electric power when a fuelcell system is started up under a low temperature condition, and, incase that a fuel cell stack of the fuel cell system is warmed up, avehicle of run permission is provided when a determination is made thatthe fuel cell stack assumes a predetermined warm-up condition bydetermining whether the fuel cell stack assumes the predeterminedwarm-up condition on the basis of one of a voltage value and an electriccurrent value of the fuel cell stack. With such a structure, since awarm-up completion decision can be accurately conducted and the timebefore warm-up completion is decided can be minimized while enablingenergy required for warm-up to be saved, the present invention isexpected to have wide applications involving a fuel cell poweredvehicle.

1. A control device of a vehicular fuel cell system, comprising: awarm-up output control section configured, when the fuel cell system isstarted up under a low temperature condition necessary for warm-up of afuel cell stack and when the fuel cell stack of the fuel cell system iswarmed up, to cause the fuel cell stack to generate electric power toallow predetermined warm-up electric power to be drawn; and a runpermission section configured to determine, during a period wherein thewarm-up electric power is drawn by the warm-up output control section,whether the fuel cell stack assumes a predetermined warm-up condition ona basis of one of (1) a voltage value and (2) an electric current valueof the fuel cell stack, wherein when a determination is made that thefuel cell stack assumes the predetermined warm-up condition, the runpermission section is configured to provide a vehicle with a runpermission, (1) when the voltage value of the fuel cell stack is equalto or more than a run available voltage value that is necessary beforethe vehicle may commence travel, wherein the run available voltage valueis obtained from predetermined current/voltage characteristics showing arelationship between the electric current value of the fuel cell stackand the run available voltage value at a temperature at which an outputvalue of the fuel cell stack is available to provide the vehicle withthe run permission, or (2) when the electric current value of the fuelcell stack is equal to or less than a run available current value thatis necessary before the vehicle may commence travel, wherein the nmavailable current value is obtained from predetermined current/voltagecharacteristics showing a relationship between the voltage value of thefuel cell stack and the run available current value at a temperature atwhich the output value of the fuel cell stack is available to providethe vehicle with the run permission.
 2. The control device according toclaim 1, wherein the run permission section provides the vehicle withthe run permission when a temperature of coolant in the fuel cell stackis equal to or more than a predetermined value.
 3. The control deviceaccording to claim 1, wherein when a temperature of coolant in the fuelcell stack is less than a predetermined value, the run permissionsection controls an auxiliary device which is provided to a power plantthat includes the fuel cell stack so as to heat the fuel cell stack. 4.The control device according to claim 3, wherein the auxiliary deviceincludes a combustor, wherein exhaust emitted from the fuel cell stackis introduced to the combustor.
 5. The control device according to claim4, wherein the combustor is provided with an electric-heated catalystsection operative to be heated to a catalytic active temperature byelectric heat, a catalytic combustor section configured to combust theexhaust, and a heat exchanger configured to allow combustion heat of theexhaust to be transferred to the coolant.
 6. A control device of avehicular fuel cell system, comprising: a warm-up output controllingmeans, when the fuel cell system is started up under a low temperaturecondition necessary for warm-up of a fuel cell stack and when the fuelcell stack of the fuel cell system is warmed up, for controlling thefuel cell stack to generate electric power to allow predeterminedwarm-up electric power to be drawn; and a run permission providing meansfor providing a vehicle with a run permission when a determination ismade that the fuel cell stack assumes a predetermined warm-up condition,wherein the run permission providing means is configured to determinewhether the fuel cell stack assumes the predetermined warm-up conditionon a basis of one of (1) a voltage value and (2) an electric currentvalue of the fuel cell stack during a period wherein the warm-upelectric power is drawn by the warm-up output controlling means, whereinthe run permission providing means is configured to provide the vehiclewith the run permission (1) when the voltage value of the fuel cellstack is equal to or more than a run available voltage value that isnecessary before the vehicle may commence travel, wherein the runavailable voltage value is obtained from predetermined current/voltagecharacteristics showing a relationship between the electric currentvalue of the fuel cell stack and the run available voltage value at atemperature at which an output value of the fuel cell stack is availableto provide the vehicle with the run permission, or (2) when the electriccurrent value of the fuel cell stack is equal to or less than a runavailable current value that is necessary before the vehicle maycommence travel, wherein the run available current value is obtainedfrom predetermined current/voltage characteristics showing arelationship between the voltage value of the fuel cell stack and therun available current value at a temperature at which the output valueof the fuel cell stack is available to provide the vehicle with the runpermission.
 7. A method of controlling a vehicular fuel cell system, themethod comprising: drawing a predetermined warm-up electric power bycontrolling a fuel cell stack to generate electric power when a fuelcell system is started up under a low temperature condition necessaryfor warm-up of the fuel cell stack and when the fuel cell stack of thefuel cell system is warmed up; and providing a vehicle with a runpermission when a determination is made that the fuel cell stack assumesa predetermined warm-up condition, while determining whether the fuelcell stack assumes the predetermined warm-up condition on the basis ofone of (1) a voltage value and (2) an electric current value of the fuelcell stack during a period in which the wane-up electric power is drawn,wherein the vehicle is provided with the ran permission (1) when thevoltage value of the fuel cell stack is equal to or more than a runavailable voltage value that is necessary before the vehicle maycommence travel, wherein the run available voltage value is obtainedfrom predetermined current/voltage characteristics showing arelationship between the electric current value of the fuel cell stackand the run available voltage value at a temperature at which an outputvalue of the fuel cell stack is available to provide the vehicle withthe run permission, or (2) when the electric current value of the fuelcell stack is equal to or less than a run available current value thatis necessary before the vehicle may commence travel, wherein the runavailable current value is obtained from predetermined current/voltagecharacteristics showing a relationship between the voltage value of thefuel cell stack and the run available current value at a temperature atwhich the output value of the fuel cell stack is available to providethe vehicle with the run permission.